The present invention relates to a vehicle that has a frame, a driving track assembly, and a pair of secondary driving assemblies mounted on opposing lateral sides of the track assembly. More specifically, the present invention relates to a vehicle that has one or more counterbalance structures for offsetting longitudinally off-center loads carried on the frame of such a vehicle.
U.S. Pat. No. 5,615,748 (which is the subject of U.S. Reissue application Ser. Nos. 09/598,530 and 09/577,261) discloses a vehicle that comprises a main frame, a track assembly that has an endless ground engaging track for driving the vehicle, and a pair of ground engaging wheels that provide for steering and aid in driving the vehicle along the ground. The vehicle of the ""748 patent combines the advantages of vehicles that are track-driven only and vehicles that are wheel-driven only into a single vehicle.
One problem that has been realized with the vehicle of the ""748 patent can be best appreciated from the manner in which the flanking wheels and the track assembly are positioned with respect to the vehicle""s center of gravity. Because steering in the vehicle of the ""748 patent is provided by the wheels, irrespective of whether the steering is performed by pivoting the wheels about vertically extending axes or rotating the wheels at different speeds, it is desirable to locate the wheels on opposing sides of the vehicle""s center of gravity. Locating the wheels on opposing sides of the vehicle""s center of gravity provides for effective and efficient control of the vehicle during steering operations. More specifically, steering of the vehicle requires less force when the vehicle""s center of gravity is located between the wheels than when the vehicle""s center of gravity is located at a point distal from the wheels.
Also, because the primary motive force in the vehicle of the ""748 patent is provided by the track assembly, it is desirable to locate the track assembly with respect to the vehicle""s center of gravity in such a manner to ensure that the vehicle""s weight is distributed relatively evenly over the parts of the track that are engaged with the ground. This ensures that the track assembly""s tractive forces are fully put to the ground along the entire length of the track portion engaging the ground. This substantially even weight distribution is important when driving on uneven terrain because this terrain may create situations wherein only certain portions of the vehicle""s track are engaged with firm ground. By providing the track with even weight distribution, the vehicle is better suited for handling such situations.
When a removable attachment is used with the vehicle of the ""748 patent, the longitudinally off-center weight of the attachment changes the vehicle""s center of gravity. For example, when a bulldozer or plow attachment is removably attached to the front end of the vehicle frame, the weight of the attachment applies a force to the frame that causes vehicle""s center of gravity to shift forwardly towards the attachment. As a result, if the weight of the attachment is heavy enough, the vehicle""s center of gravity will no longer be located between the flanking wheels. This results in a loss of steering efficiency and affects the vehicle""s overall control. Further, the change in the vehicle""s center of gravity will result in the vehicle""s weight being distributed unevenly over the portions of the track engaged with the ground. This creates the situation described above and increases the difficulty of handling the vehicle over soft or uneven terrain.
It should be noted that the above-described undesirable situation can be created by the application of any longitudinally off-center load to the frame. For example, if the vehicle were designed for harvesting with a fixed hopper on one end thereof, filling of the hopper with harvested articles would increase the load at that end, thus creating a longitudinally off-center loading situation. As with the removable function attachment, this loading situation will also move the vehicle""s center of gravity away from its normal position thereof and towards the hopper.
Consequently, there exists a need for a way to offset the changes in the vehicle""s center of gravity created by the application of longitudinally off-center loads to the vehicle.
It is therefore the object of the present invention to meet the above-described need. To meet this object, the present invention provides a vehicle comprising a main frame having first and second opposing longitudinal end portions and a driving track assembly mounted to the main frame and including an endless ground engaging track that extends generally in a longitudinal direction of the vehicle. The frame is constructed and arranged to carry a longitudinally off-center load thereon that applies a force to the frame tending to shift a center of gravity of the vehicle towards the first longitudinal end portion thereof. This load may be applied by a removable functional attachment which is removably attached to the frame or by one or more objects, such as hay bales or a hopper containing harvested articles, that are carried on the vehicle for transport. The invention is designed to accommodate for any type of longitudinally off-center load.
The vehicle further comprises pair of secondary driving assemblies mounted to the frame on opposing lateral sides of the track assembly in flanking relation. Each of the secondary driving assemblies includes a ground engaging driving structure spaced laterally from the endless track. An engine assembly is constructed and arranged to supply power to the track assembly and the secondary driving assemblies. The driving track assembly is constructed and arranged to move the endless track using power supplied from the engine assembly to affect a vehicle driving operation wherein the endless track engages the ground to drive the vehicle in the longitudinal direction of the vehicle. Each of the secondary driving assemblies is constructed and arranged to operate the ground engaging driving structures using power supplied from the engine assembly so as to impart force to the vehicle. A steering system is operatively connected to the secondary driving assemblies and is constructed and arranged to control operation of the secondary driving assemblies so as to affect a vehicle steering operation wherein the ground engaging driving structures are operated to turn the vehicle with respect to the longitudinal direction.
The vehicle further comprises counterbalance structure movably mounted to the main frame. The counterbalance structure is movable from a normal, inoperative position through a range of operating positions wherein in each of the operating positions the counterbalance structure applies a counterbalancing force to the frame that tends to shift the vehicle""s center of gravity towards the second longitudinal end portion of the frame. The vehicle is constructed and arranged such that, in the absence of the aforesaid longitudinally off-center load being carried on the frame and with the counterbalance structure in the normal, inoperative position thereof, the vehicle has a normal center of gravity (a) located with respect to the track assembly in such a manner that a portion of the vehicle""s total weight borne by the track assembly is distributed substantially evenly over the parts of the endless track that engage the ground and (b) located laterally between the ground engaging driving structures. The counterbalance structure is constructed and arranged such that the counterbalancing force applied by the counterbalance structure to the frame varies as the counterbalance structure is moved through the range of operating positions so that, when the aforesaid longitudinally off-center load is carried on the frame, the counterbalance structure can be moved to a corresponding one of the operating positions that enables the counterbalancing force applied to the frame by the counterbalance structure to substantially offset the force applied by the load in such a manner that the vehicle""s center of gravity remains at or near the normal location thereof.
The advantage of the provision of one or more counterbalance structures is that it allows longitudinally off-center loads of varying magnitudes to be carried by the vehicle of the present invention without significantly sacrificing performance or control. In particular, the counterbalance structure can be repositioned through its range of positions to offset the varying forces applied by different longitudinally off-center loads and maintain the vehicle""s center of gravity in its best desirable longitudinal position with the wheels on opposing sides thereof.
A related aspect of the invention provides a method for counterbalancing a longitudinally off-center load in the type of vehicle discussed above. The method comprises applying a longitudinally off-center load on the main frame such that the load applies a force to the frame that tends to shift the vehicle""s center of gravity away from the normal location thereof towards the first longitudinal end portion of the frame; and moving the counterbalancing structure to an operating position whereat the counterbalancing force applied to the frame by the counterbalance structure substantially offsets the force applied to the frame by the longitudinally off-center load in such a manner that the vehicle""s center of gravity remains at or near the normal location thereof.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.